Description of Business - Summary of Allocated Purchase Price Parenthetical) (Details) - JMB $ in Millions	Mar. 19, 2021 USD ($)
Description Of Business [Line Items]
Operating lease liabilities	$ 3.0
Excess fair value of intangibles other than goodwill	$ 20.8

Business combination recognized identifiable assets acquired and liabilities assumed operating lease liabilities.

No definition available.

Name:	amrk_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilities
Namespace Prefix:	amrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant